Climbing Stairs

class Solution {
    public int climbStairs(int n) {
        if(n==0 || n==1 || n==2) {
            return n;
        }

        int[] cache = new int[n+1];
        for(int i=0; i<=2; i++) {
            cache[i] = i;
        }
        for(int i=3; i<=n; i++) {
            cache[i] = -1;
        }
        return climb(n, cache)[n];
    }

    private int[] climb(int n, int[] cache) {
        int steps = 0;

        if(n-1 >= 0) {
            if(cache[n-1] >= 0) {
                steps += cache[n-1];
            } else {
                cache = climb(n - 1, cache);
                steps += cache[n-1]; // climbing one step
            }
        }
        if(n-2 >= 0) {
            if(cache[n-2] >= 0) {
                steps += cache[n-2];
            } else {
                cache = climb(n - 2, cache);
                steps += cache[n-2]; // climbing two steps
            }
        }
        cache[n] = steps;
        return cache;
    }
}